Path animation ease (non-linear speed)?
Look in the properties panel of your Graph Editor (displayed with N), it looks like you've automatically generated a Modifier > Generator. You can modify it but you won't be able to add keyframes or manipulate handles. So:


Close it.
Create 2 keyframes at frame 1 and frame n:
On the Timeline, put your cursor at frame 1 and give the Evaluation Time of your curve a value of 0 and insert a keyframe with i.
On the Timeline, put your cursor at frame X (for example 50) and give the Evaluation Time of your curve a value of 100 (for example) and insert a keyframe with i.
Now, in your Graph Editor, you can see the curve and handles that have been created, you can manipulate the handles, change their type with V or create new keyframes with i.